The present invention relates to a bearing apparatus and a producing method thereof, and more particularly, to a bearing apparatus and a producing method thereof which are preferably used for a hub unit for a vehicle such as an automobile.
A hub unit for a vehicle will be explained. The hub wheel has a hollow shaft. An inner ring of a rolling bearing is mounted to an outer periphery of the hollow shaft by press-fit. A shaft end of the hollow shaft is caulked on the outer end surface of the inner ring by bending the shaft end outwardly in a diametrical direction. The bearing is prevented from slipping off from the hollow shaft by this caulked portion. A pre-load is applied to the inner ring of the bearing by this caulking.
A load is applied to the hollow shaft by the pressure-fit of the inner ring of the bearing. The hollow shaft is formed around its outer periphery with a hardened layer due to heat by quenching or the like in order that the hollow shaft has the structure that can bear the load. On the other hand, the shaft end of the hollow shaft remains in a stage of being caulked on the outer end surface of the inner ring, i.e., the shaft end is not hardened.
A range of the hardened layer formed on the outer periphery of the hollow shaft is limited to a certain degree.
However, in the range where the hardened layer is formed, a position of the caulked side end portion in the axial direction is not clearly defined. Thus, when it is processed to be hardened, the position of the caulked side end portion of the hardened layer in its add is prone to be an incorrect position closer to an outer end or to inner end in the axial direction from the limited range.
If the position of the end portion in the axial direction of the hardened layer is positioned incorrectly with respect to the hollow shaft, a gap may be generated between an inner peripheral surface of the inner ring and an outer peripheral surface of the hollow shaft caulked on the outer end surface thereof in some cases. This gap deteriorates creep resistance.
Therefore, a caulking auxiliary jig is previously inserted on the side of the inner periphery of the hollow shaft before caulking, thereby preventing the gap from being generated. Further, after the caulking, the inner periphery of the hollow shaft is again worked. Such a gap-preventing operation of the hollow shaft increases the number of producing steps and cost of the hub unit.
Thus, it is a main object of the present invention to provide a bearing apparatus of a hub unit, and the like, for a vehicle, capable of appropriately managing a position of an end portion, in the axial direction, of a hardened layer formed on an outer periphery of a hollow shaft.
Other objects, features and merits of the present invention will be apparent from the following description.
The present invention is, in sum, described as follows. A bearing apparatus of the present invention includes a hollow shaft provided around its outer peripheral surface with a bearing fitting region, and a rolling bearing having an inner ring fitted around the bearing fitting region of the hollow shaft. A shaft end of the hollow shaft is bent outwardly in a diametrical direction, thereby being caulked on an outer end surface of the inner ring of the rolling bearing.
The bearing fitting region has a hardened layer in its region from an inner end surface corresponding position of the inner ring of the rolling bearing to a portion before an outer end surface corresponding position. The bearing fitting region further has a non-hardened layer in its region from the portion before the outer end surface corresponding position of the inner ring to the shaft end of the hollow shaft.
A position of a caulked side end portion of the hardened layer is defined based on the following relational expression (1):
((Axe2x88x92Cxe2x88x92D)Y/E)xe2x89xa6X less than (Axe2x88x92C)xe2x80x83xe2x80x83(1)
wherein A represents a width in the axial direction of the inner ring, C represents a chamfering length in the axial direction in the outer end surface of the caulked side of the inner ring, D represents a chamfering length in the axial direction in an outer end surface of the inner ring, E represents a thickness of the hollow shaft, X represents a distance from a position of the chamfering length D to the caulked side end portion of the hardened layer, and Y( less than E) represents a hardening treatment depth.
With this defining expression, appropriate hardening treatment can be carried out by applying concrete numerical values to the respective length in the axial direction of the inner ring and the thickness of the hollow shaft. Further, it is possible to reduce the number of steps and time of the producing operation of the bearing apparatus, such as a hub unit, and to enhance the productivity.
In the present invention, preferably, the hollow shaft is a hub wheel, the rolling bearing is a double row angular contact ball bearing with vertex of contact angles outside of bearing or a double row tapered roller bearing with vertex of contact angles outside of bearing.
These and other objects, as well as advantages, of the invention will become clear by the following description of preferred embodiments of the invention with reference to the accompanying drawings, wherein like components are indicated by the same numerals.